1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a transflective liquid crystal display device and a fabricating method thereof. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for simplifying a fabrication process and improving a production yield.
2. Discussion of the Related Art
Generally, transflective liquid crystal display (LCD) devices function as both transmissive and reflective LCD devices. Since the transflective LCD devices can use both a backlight and the exterior natural or artificial light, the transflective LCD devices are not restricted from the circumstances, and a power consumption of the transflective LCD devices can be reduced.
FIG. 1 is a schematic perspective view of a transflective liquid crystal display device according to the related art.
In FIG. 1, a transflective liquid crystal display (LCD) device 29 includes first and second substrates 30 and 15 facing into and spaced apart from each other, and a liquid crystal layer 23 interposed therebetween. A switching element “T” and array lines 34 and 46 are on the inner surface of the first substrate 30. A pixel electrode including a reflective electrode 52 and a transparent electrode 64 is formed in a pixel region “P” of the first substrate 30. The reflective electrode 52 has a transmissive hole “A”. The pixel electrode except for the transmissive hole “A” functions as a reflective portion “C”. A black matrix 19 and a sub-color filter 17 are formed on the inner surface of the second substrate 15. A common electrode 13 is formed on the black matrix 19 and the sub-color filter 17.
FIG. 2 is a schematic cross-sectional view of the transflective liquid crystal display device according to the related art.
In FIG. 2, a transflective liquid crystal display (LCD) device 29 includes first and second substrates 30 and 15, a liquid crystal layer 23 interposed therebetween, and a backlight unit 41 under the first substrate 30. A pixel electrode including a transparent electrode 64 and a reflective electrode 52 are formed on the inner surface of the first substrate 30. The reflective electrode 52 has a transmissive hole “A”. Even though the reflective electrode 52 is formed over the transparent electrode 64 in FIG. 2, the reflective electrode can be formed under the transparent electrode. A common electrode 13 is formed on the inner surface of the second substrate 15.
In a reflective mode, the transflective LCD device 29 uses the exterior natural or artificial light. An incident light “J” passing through the second substrate 15 is reflected at the reflective electrode 52 and then passes through the liquid crystal layer 23 aligned by an electric field between the reflective electrode 52 and the common electrode 13. Images are displayed by modulating an intensity of the incident light “J” and the reflected light according to the alignment of the liquid crystal layer 23.
In a transmissive mode, light “F” from the backlight unit 41 under the first substrate 30 is used. The light “F” emitted from the backlight unit 41 enters the liquid crystal layer 23 through the transparent electrode 64. The liquid crystal layer 23 is aligned by an electric field between the transparent electrode 64 and the common electrode 13, and images are displayed through the transmissive hole “A” by modulating an intensity of the light “F” from the backlight unit 41 according to the alignment of the liquid crystal layer 23.
FIG. 3 is a schematic plane view showing an array substrate for the transflective liquid crystal display device according to the related art.
In FIG. 3, a thin film transistor (TFT) “T”, which is a switching element, is disposed on a substrate 30 in a matrix. The substrate 30 is referred to as an array substrate. A gate line 34 and a data line 46 crossing each other are connected to the TFT “T”. A pixel region “P” is defined at each intersection of the gate line 34 and the data line 46. A reflective layer 52 having a transmissive hole “A” is formed in the pixel region “P”. A storage capacitor “S” is formed at a portion of the gate line 34 and electrically connected to a transparent pixel electrode 64 in parallel. A gate pad 36 and a data pad 48 are formed at the ends of the gate line 34 and the data line 46, respectively. Signals are applied to the gate pad 36 and the data pad 48 from an external circuit (not shown). The TFT “T” includes a gate electrode 32, an active layer 40 over the gate electrode 32, and source and drain electrodes 42 and 44.
FIGS. 4A to 4D are schematic cross-sectional views showing the fabricating method of the array substrate for the transflective liquid crystal display device according to the related art. FIGS. 4A to 4D are taken along line IV-IV of FIG. 3.
In FIG. 4A, after depositing a conductive metal layer on a substrate 30, a gate electrode 32, a gate line 34 (shown in FIG. 3), and a gate pad 36 at one end of the gate line 34 (shown in FIG. 3) are formed through the first mask process. A first insulating layer 38 is formed on the gate electrode 32, the gate line 34 (shown in FIG. 3), and the gate pad 36. A semiconductor layer 40 including an active layer 40a of amorphous silicon and an ohmic contact layer 40b of impurity-doped amorphous silicon is formed on the first insulating layer 38 over the gate electrode 32 through the second mask process. The semiconductor layer 40 has an island shape.
In FIG. 4B, after depositing a conductive metal layer on the ohmic contact layer 40b, source and drain electrodes 42 and 44, a data line 46, and a data pad 48 are formed through the third mask process. The source electrode 42 is connected to the data line 46, and the data pad 48 is formed at one end of the data line 46. A capacitor electrode 50 (shown in FIG. 3) of an island shape is formed on the gate line 34 (shown in FIG. 3). The capacitor electrode 50 (shown in FIG. 3) may not be formed on the gate line 34. A second insulating layer 48 is formed on the source and drain electrodes 42 and 44. After depositing a metallic material layer having high reflectance such as aluminum (Al) on the second insulating layer 50, a reflective layer 52 having a transmissive hole “A” in the pixel region “P” is formed through the fourth mask process.
In FIG. 4C, after a third insulating layer 54 is formed on the reflective layer 52, a drain contact hole 56 exposing the drain electrode 44, an open portion 58 corresponding to the transmissive hole “A”, a gate pad contact hole 60 exposing the gate pad 36, and a data pad contact hole 62 exposing the data pad 48 are formed through the fifth mask process.
In FIG. 4D, after depositing a transparent conductive material on the third insulating layer 54, a pixel electrode 64, a gate pad terminal 66, and a data pad terminal 68 are formed through the sixth mask process. The pixel electrode 64 is connected to the drain electrode 44 and formed in the pixel region “P”. The gate pad terminal 66 and the data pad terminal 68 are connected to the gate pad 36 and the data pad 48, respectively.
FIG. 5 is a schematic cross-sectional view of the transflective liquid crystal display device including the array substrate of FIG. 4D according to the related art.
In FIG. 5, the transflective liquid crystal display device includes a transmissive portion “t” and a reflective portion “r”. To improve the light efficiency of the transmissive portion “t” and the reflective portion “r”, a first cell gap “d1” of the transmissive portion “t” is formed to be double of a second cell gap “d2” of the reflective portion “r”. The first and second cell gaps having different values in the transmissive portion and the reflective portion are referred to as a dual cell gap. Two methods to form the dual cell gap are suggested. The first method for the dual cell gap is to form a step in the first substrate, and the second method is to form a step in the second substrate. Recently, methods to form steps in the first and second substrates are mainly used for the dual cell gap.
In FIG. 5, even though the first cell gap “d1” of the transmissive portion “t” is formed to be double of the second cell gap “d2” of the reflective portion “r”, reflection efficiency is poor because a reflective layer 52 is a mirror type. When the reflective layer 52 is an uneven surface type instead of a mirror type, the reflection efficiency of the reflective portion “r” is improved due to scattering phenomenon at the reflective layer 52. Accordingly, it is necessary to form a dual cell gap for improving the light efficiency of reflective and transmissive portions and an uneven surface for improving the reflection efficiency of a reflective electrode at the same time in an LCD device.